Sig FCU differences/simalarities between 365/XL and P320

Since a few of us asked in another and didn't want to get way off topic I figure I will ask in it's own thread. Are the FCU's between the Sib P320 series and P365/XL series the same design just smaller or are they different? If they are different in design can anyone illuminate the differences preferably with photo or diagrams if possible.

I am most interested as I own a 365 and plan to get a XL when I can find one reasonably priced. I have never owned or had much time on a 320 but I am aware of drop discharge issue with the 320 but no safety issues with the 365 series other than early reliability and firing pin issues.

I like the 365 for my small hands and like the modular design Sig uses (along with others). I would love to see a full size or larger than the XL version of the 365. The lower bore axis and small grip and trigger reach dimensions are a boon to small hands and can be done away with larger grip modules if needed by large handed users but the same doesn't work for the 320.

I didn't think I would answer my own post but I found some detailed P320 and P365 FCU disassembly and assembly videos and they are different more than just the 365 being smaller. They use different springs in different orientations. The 320 uses a different slide lock lever layout and a coil spring held in by a horizontal lateral pin where the 365 uses a wire like spring in the FCU chassis and the takedown lever arm to hold the slide lock lever in place and give it spring tension. The disconnector is in slightly different location on each and a different size and shape. Same with the firing pin safety lever that pushes up on the firing pin safety plunger in the slide. The 320 FCU has a separate housing for the sear assembly whereas the 365 sear fits into the FCU chassis directly. The 320 FCU goes into the grip module then the take down lever is pushed through a hole in the grip module and FCU. The 365 has the take down lever in place in the FCU and the whole assembly is placed in the grip module as a complete unit. There are probably more differences but those are what I noted form watching the videos so far.

This is the P320 FCU assembly video. https://www.youtube.com/watch?v=lTQBJbh9d7k&t=676s

These are the disassembly and assembly videos for the P365.

https://www.youtube.com/watch?v=_4fYndURvl8

https://www.youtube.com/watch?v=1TeTuMNyaFA

I could be wrong but it looks like the 365 FCU is a machined chassis and the P320 chassis is stamped. There function is similar but not identical.


ETA here is a much clearer video of the 365 FCU disassembly
https://www.youtube.com/watch?v=TFVyvqdpouA&t=619s

Attachment 82234

They 320 and the 365 are similar but different designs. The most obvious difference bring the P320 FCU is stamped sheet metal and the 365 FCU is a casting which is then finish machined.

Quote:

---

Originally Posted by GJM

Attachment 82234

---

Thanks for the pics. I have since picked up a 365Xl to go with my 365. That angle picture really shows the difference in width and chassis design differences well.

I had forgotten this useful thread was started by @octagon to keep the "P320 vs. P365 FCU" contrasts out of the main P320 thread. I am guilty of not remembering to put my recent comments on this here, instead of mucking up that discussion, and I apologize.

Having two P365's, I am pretty interested in this topic, as it relates to safety in general and the differences in the two FCU designs in particular. I'll try and put any content related to that here from now on.

Dragging in a post from a couple days ago I should have put here:

Quote:

---

Originally Posted by RJ

I have been troubled the last few days seeing the P320 FCU get dissected by the Armorer's here, with some nagging doubts about how much all this may, or may not, be seen in my two P365s.
Obviously getting redirected by experts like @HCM and others about the lack of NDs with the P365 was comforting. Hearing other armorers like @KevH and @lwt16 was also extremely helpful. But I still had these scary weird thoughts in the deep crevices of my lizard brain about all this, because as a hands on learner I didn't "know", in touchy-feely terms. Being fairly risk averse by nature, I was seriously wondering about whether I'd have to rejoin GSSF.

So I just spent a useful hour comparing one of my P365 FCUs with the Sig Guy's P365 and P320 FCU disassembly videos, which was the best source I could fine online. I didn't take any parts off my P365 FCU, that was a bit too scary. But I was really struck by how different in execution the two FCUs are. Obviously these are uneducated comments by a random .civ geezer, and I only had the 320 video to compare, but I was shocked, really, by how "agricultural" the P320 FCU was designed/assembled/put together by comparison. The P365 parts and housing looked tightly built, to reasonably accurate tolerances (I assume lots of MIM parts); the P320 looked like it was done by a high school shop class in metal stamping. The 320 TRS is hanging out in the open, almost as an afterthought, the P365 spring is tucked in and under the FCU. The ejector on the P365 is this solid piece of MIM molded into the body of the FCU, the ejector on the 320 is a little steel protrusion stamped when the sheet metal is formed. The P320 sear housing is a little assembly that inserts into the back of the FCU, the sear in the P365 runs within a purpose-milled area at the back of the FCU. I also looked in detail at the firing pin safety block operation in the P365. I also checked my holsters, and the tight fit (JM CK, Vedder, RCS) offers adequate protection against a foreign object ND far as I can tell. I'd never looked quite so closely at my FCU before and this was really eye opening, for me. Decided to keep the P365s and get on with life.

---